Populate select box from database query based on another select box using only 1 table

Hi guys I am currently creating a website with the main function of booking cars. Therefore the user would be first able to select a car category from the database query which will output the selected car category names. After selecting the car category name, the second select box would then by dynamically updated with a new set of of car names that are associated with the category.

There may have been many similar questions to this however for the website NO jQuery or AJAX can be utilized. And other questions and examples often utilize 2 or more tables however I am using only 1 table for this function.

Without using Ajax or over complicating things with complex json iteration you could try along these lines. It should be noted that embedding the $_GET variable directly in the sql is not the best option - prepared statements would be better but should give the idea.